With the recent demand for soundproofing material for vehicle having a lighter weight, felt-based light weight soundproofing materials have been mainly used in place of related art heavy sheets made of EPDM, olefin or the like. Felt has excellent sound absorbing properties but has poor sound barrier properties. In order to eliminate this shortcoming, it has heretofore been practiced to compress felt so that it becomes less air-permeable.
On the other hand, Japanese Patent No. 3498085 cited below discloses a soundproofing material having an ultralight weight obtained by bonding a sound absorbing layer such as felt and a resonance layer such as film to each other with an adhesive at a predetermined adhesion. However, this soundproofing material is disadvantageous in that it has a two-layer structure and thus can difficultly absorb noise in the cabinet. Further, this soundproofing material is also disadvantageous in that its rigidity is too small for dash silencer to attain required shape stability.
Further, Japanese Patent Publication No. Patent No. 2001-347900 and Japanese Patent No. 3264230 each disclose a three-layer soundproofing material comprising a sound absorbing layer such as felt provided on the both sides of an air-impermeable film. However, since this kind of a multi-layer soundproofing material is obtained by bonding a film and a sound absorbing layer to each other with either of these layers impregnated or coated with an adhesive, it is disadvantageous in that the production method involves additional steps that add to the cost and the resulting soundproofing material can be difficultly formed into a free three-dimensional shape following the shape of the vehicle body.
It is therefore an object of the present invention to provide a soundproofing material for vehicle having a light weight, a small thickness and excellent soundproofing properties which can be easily formed into a free three-dimensional shape and can be produced at reduced cost.